This application relates generally to interconnection systems, such as those including electrical connectors, used to interconnect electronic assemblies.
Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system as separate electronic assemblies, such as printed circuit boards (“PCBs”), which may be joined together with electrical connectors. A known arrangement for joining several PCBs is to have one PCB serve as a backplane or a motherboard. Other PCBs, called “daughterboards” or “daughtercards”, may be connected through the backplane or to the motherboard. As a specific example, a computer system may be assembled with a motherboard containing a processor and memory on a daughterboard.
Backplanes or motherboards may be made as PCBs onto which connectors are mounted. Conducting traces in the PCB may be electrically connected to signal conductors in the connectors so that signals may be routed through the connectors to components on or connected to the backplane or the motherboard. Daughtercards may also have connectors. A connector mounted on a daughtercard may be plugged into a connector mounted on the backplane or motherboard.
Alternatively, daughtercards may include contacts at an edge and can be directly connected to backplane or motherboard connectors. In this configuration, connectors mounted on the backplane or motherboard include slots into which the edges of the daughtercards are inserted. Compliant terminals in the connectors engage the contacts of the cards. Such connectors are sometimes referred to as card edge connectors.
FIG. 1A illustrates an electrical assembly comprising a card edge connector 100 with a conventional design. Motherboard 101 is connected to daughtercard 103 through card edge connector 100. Connector 100 includes a plurality of conductive elements 104 held by a housing 102. Housing 102 has an opening 112 into which daughtercard 103 is inserted. The conductive elements 104 are positioned within housing 102 such that they will make contact with pads on daughtercard 103 when inserted into opening 112. FIG. 1B shows a cross-section view of the card edge connector in FIG. 1A. Each conductive element 104 comprises a contact portion 106 and a tip 108 extending from the contact portion.
In operation, an edge of a daughtercard will be inserted into opening 112. That insertion will deflect the conductive element. The mating portion of the conductive element is a beam such that deflecting the beam causes the mating portion to generate a spring force against a pad on the surface of the daughter card. The amount of spring force depends on the properties of the conductive element as well as the amount the conductive element is deflected from its rest state in which no force is applied to the conductive element.
To increase the amount of the spring force generated, the conductive elements may be configured, such as by deforming the conductive elements or mounting the conductive element, to increase the amount that the conductive element is deflected from its rest state to be positioned in the mated configuration. At its rest state, a conductive element may be offset, in a direction opposite the direction in which the conductive element is deflected, relative to its position when mated to a pad on a card.
When the conductive element is configured in this way, at its rest state, the tip of the conductive element would be positioned in a path of a card being inserted into the connector. To ensure that the edge of the card does not hit the tips of the conductive elements, housing 102 may be configured to hold the tips of the conductive elements away from the center of opening 112. FIG. 1B illustrates shelves 110 that engage tips 108 of the contacts. In this way, the conductive elements are spread, such that they are not in opening 112 and cannot be struck by an edge of a board inserted into slot 112. This process of mounting a conductive element to increase its contact force in the mated position, yet spreading the tips of the conductive elements while in an unmated configuration, is sometimes referred to as “preloading”.
Electronic systems generally have gotten smaller, faster, and functionally more complex. Because of these changes, the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. Measures of signal integrity (SI) of conventional card edge connectors deteriorate at high speeds and at high densities, creating challenges in the design of card edge connectors for modern electronic assemblies.